AP®ChemistryCollege BoardStudy GuidesUnit 1: Atomic Structure & PropertiesMoles & Molar MassThe Mole Concept

The Mole Concept (College Board AP® Chemistry)

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The Mole Concept

  • The number of particles that react in a chemical experiment cannot be directly determined because the size and mass of an individual particle is so small

  • Moles are used to relate the mass of a sample to the number of particles it contains

  • The mole (mol) is the SI unit for the amount of substance

  • The number of moles (n) of a substance and the number of constituent particles or formula units it contains are related by Avogadro’s number (NA)

NA = 6.022 x 1023 mol-1

Number of constituent particles = NA x n

1 mole of…

Fe atoms

H2O molecules

Al2(SO4)3 formula units

Contains…

6.022 x 1023 Fe atoms

1.2044 x 1024 H atoms

6.022 x 1023 O atoms

1.2044 x 1024 Al3+ ions

1.8066 x 1024 SO42- ions

Examiner Tip

Note that some textbooks will use the terms Avogadro’s constant and Avogadro’s number interchangeably.

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    Fallon

    Author: Fallon

    Expertise: Chemistry Content Creator

    Fallon obtained a double major in chemistry and secondary education, and after graduating she taught Chemistry and Organic Chemistry for 7 years. Fallon’s passion for creating engaging classroom materials led her to pursue a career in content development. For over 3 years, Fallon has created videos, review materials, and practice questions for AP Chemistry, IGCSE, and other international exam boards.